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From "Christiaan des Bouvrie" <c.des.Bouv...@CostEngineering.eu>
Subject Re: getAllReferencingObjects(Object object) request
Date Mon, 18 Jun 2007 08:30:51 GMT
Hi David and Matthew,

 

Thanks for the response. Regarding the design issues, I agree that it is
a Java problem. In jdo this problem becomes more evident. If I want to
delete an object in java, I need to set all references to null. In JDO I
need to set all references to null and actually delete the object. I
noticed that a lot of beginners with JDO assume that when deleting the
objects the other part, setting references to null, is done
automatically, which is not the case. In any case it is something which
needs to be dealt with and it is now left to the developer to do it.
What I do now is that for each object I determine which objects are
referencing it. This usually comes down to executing queries where I
check whether a certain attribute is or contains the object. I figured
with all the available jdo meta data this could be something that can be
done by the framework? Moreover, this code easily breaks on refactoring.
That would also be nicely solved if the jdo metadata is used.

 

Regarding the performance, I am not sure what makes this solution slower
than the current solution, doing it yourself, that is, if my assumption
that it can be done with the jdo metadata is correct. Collecting the
metadata is probably a fraction of the actual time to delete the object
in the datastore. So the performance decrease will be caused by querying
attributes which could possibly contain the object according to the
metadata, but which you as a developer know is not the case. I would say
if performance becomes a problem in that case you can always go back by
doing it yourself, or provide some extra metdata to
getAllReferencingObjects so these classes can be skipped.  This is also
the approach I have currently. I first use my generic delete algorithm
to recursively determine what needs to be deleted and what references
need to be updated. If I notice or know this will be slow due to a large
collection of objects I will switch to a delete-by-query and optimize
the number of objects that need to be updated. But again, it is hardly
ever considered slow due to the getAllReferencingObjects(), but more due
to the actual deleting of large collections of objects using
pm.deletePersistentAll().

 

Kind regards,

Christiaan


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